1. Field of the Invention
This invention generally relates to the field of signal processing and communications. More particularly, the present invention relates to embedding data into an audio signal and detecting data embedded into an audio signal.
2. Description of Background Information
The efficient and secure storage and distribution of digital audio signals are becoming issues of considerable importance for the information revolution currently unfolding. The challenges of the storage and distribution of such signals arise particularly from the digital nature of modern audio. Most modern digital audio allows for the creation of unlimited, perfect copies and may be easily and massively distributed via the Internet. Nevertheless, such digital nature also makes possible the adoption of intelligent techniques that can contribute in the control of unauthorized copying and distribution of multimedia information comprising audio. In addition, opportunities arise whereby digital audio may be used as a medium for the delivery of enhanced services and for a more gratifying audio and/or visual experience.
The efficient and secure storage and distribution of digital audio signals are becoming issues of considerable importance for the information revolution currently unfolding. The challenges of the storage and distribution of such signals arise particularly from the digital nature of modern audio. Most modern digital audio allows for the creation of unlimited, perfect copies and may be easily and massively distributed via the Internet. Nevertheless, such digital nature also makes possible the adoption of intelligent techniques that can contribute in the control of unauthorized copying and distribution of multimedia information comprising audio. In addition, opportunities arise whereby digital audio may be used as a medium for the delivery of enhanced services and for a more gratifying audio and/or visual experience.
Audio delivery through a network (e.g., the Internet), presented as a stand-alone service or as part of a multimedia presentation, comes in a large range of perceived qualities. Signal quality depends on the audio content (e.g., speech and music), the quality of the original recording, the available channel bandwidth, and real-time transmission constraints.
Real-time Internet audio usually applies to broadcasting services. It is generally achieved by streaming audio, which is decoded at a receiving workstation. Real-time transmission requirements impose limitations on signal quality. At present, audio streaming delivers quality comparable to AM radio.
By relaxing real-time constraints, new opportunities for services have appeared where the quality and security of the transmitted audio is enhanced. Such services include the secure downloading of CD-quality music at transmission rates that are too high for real-time transmission but lower than the CD standard. Such signal compression capitalizes on psychoacoustic properties of human hearing.
Security and authentication of audio distributed over networks (e.g., non-homogeneous networks) is also often required, in addition to low bit rates that do not compromise audio quality. Moreover, perceptual coding may be used for the insertion of new, secure information to an original audio signal in a way that this information remains inaudible and extractable by secure means. This process is generally referred to as watermarking.
Simultaneous frequency masking is used to implement perceptual coding and transparent watermarking in digital audio. Frequency masking is a property of hearing that renders audio signal components in a frequency region inaudible if a component of higher energy is in the same vicinity. The ability of the dominant component to mask others depends on its relative energy and on its proximity to the other audio signal components. In addition to simultaneous frequency masking, temporal masking is used to reduce pre-echoes and post-echoes resulting from signal processing.
While masking in the power spectrum of auditory signals dominates audio coding and watermarking techniques, the phase information has not been involved to date (see, e.g., Nyquist & Brand, Measurements of Phase Distortion, BELL SYS. TECH. J., Vol. 7, 522–49 (1930); D. Preis, Phase and Phase Equalization in Audio Signal Processing—A Tutorial Review, J. AUDIO ENGINEERING SOCIETY, Vol. 30, No. 11, 774–94 (1982)).